[RFC] LE based Remote Name Request

[RFC] LE based Remote Name Request

[Brian Gix]

LE does not have a Remote Name Request like BR/EDR has.  It does have 
the ability to fairly efficiently request the remote device name, 
however, which we should implement.  Currently the only support we offer 
for obtaining the remote device name is to pluck it out of the 
Advertising packets (Formatted identically to EIR) which works for most 
devices, but as with BR/EDR, there is no requirement that devices 
include their name in their advertising data.

The Device Name characteristic is Mandatory, and may only exist once for 
a device.  If it is less than 20 bytes may therefore be read with a 
single ReadByType GATT command (uuid16: 0x2a00) over the full 1-0xFFFF 
range. It must also be readable without security, so can be done without 
first going through SMP.

We may not want to featurize this particular functionality at all, since 
all of the components to obtain this info is already available: We just 
need to set up an ATT socket in BlueZ, and make the request.  However, 
when we talk about Scanning for devices, and automatically forwarding 
the Remote Name via a MGMT evevnt, the precedence is there to supply it 
from the kernel.  And if we were to go down that path, we would also 
want to simultaneously offer access to the equally Mandatory and 
Unsecured "Appearance" Characteristic (uuid16: 0x2a01) which is LE's 
sort-of equivilent to the BR/EDR Class-Of-Device.

So: What are the feelings about doing Remote Name (And Appearance) 
discovery in the kernel, probably as part of the LE Discovery mechanism? 
  I favor putting it in the kernel, due to the equivalent functionality 
available to BR/EDR there.

Also, there is no coincidence that I offer this RFC at the same time as 
I bring up the Write Signed Command functionality from earlier today. 
Both concern usages of GATT (or at least ATT) in a way not currently 
supported. It is also a case where ideally, we would use a low-latency 
connect-read-disconnect methodology.

-- 
Brian Gix
bgix@codeaurora.org
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum

Re: [RFC] LE based Remote Name Request

[Vinicius Costa Gomes]

Hi Brian,

On 11:39 Fri 18 Nov, Brian Gix wrote:
> 
> LE does not have a Remote Name Request like BR/EDR has.  It does
> have the ability to fairly efficiently request the remote device
> name, however, which we should implement.  Currently the only
> support we offer for obtaining the remote device name is to pluck it
> out of the Advertising packets (Formatted identically to EIR) which
> works for most devices, but as with BR/EDR, there is no requirement
> that devices include their name in their advertising data.
> 
> The Device Name characteristic is Mandatory, and may only exist once
> for a device.  If it is less than 20 bytes may therefore be read
> with a single ReadByType GATT command (uuid16: 0x2a00) over the full
> 1-0xFFFF range. It must also be readable without security, so can be
> done without first going through SMP.
> 
> We may not want to featurize this particular functionality at all,
> since all of the components to obtain this info is already
> available: We just need to set up an ATT socket in BlueZ, and make
> the request.  However, when we talk about Scanning for devices, and
> automatically forwarding the Remote Name via a MGMT evevnt, the
> precedence is there to supply it from the kernel.  And if we were to
> go down that path, we would also want to simultaneously offer access
> to the equally Mandatory and Unsecured "Appearance" Characteristic
> (uuid16: 0x2a01) which is LE's sort-of equivilent to the BR/EDR
> Class-Of-Device.
> 
> So: What are the feelings about doing Remote Name (And Appearance)
> discovery in the kernel, probably as part of the LE Discovery
> mechanism?  I favor putting it in the kernel, due to the equivalent
> functionality available to BR/EDR there.

I am in favor of this, more because of the Appearance than the Name 
discovery. The Name most well behaved devices will provide through
the Advertising Data, Appearance we can only discover via GATT and
it is very useful for the user.

> 
> Also, there is no coincidence that I offer this RFC at the same time
> as I bring up the Write Signed Command functionality from earlier
> today. Both concern usages of GATT (or at least ATT) in a way not
> currently supported. It is also a case where ideally, we would use a
> low-latency connect-read-disconnect methodology.
> 
> -- 
> Brian Gix
> bgix@codeaurora.org
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


Cheers,
-- 
Vinicius

Re: [RFC] LE based Remote Name Request

[Chen Ganir]

Brian, Vinicius,

On Sat, Nov 19, 2011 at 00:08, Vinicius Costa Gomes
<vinicius.gomes@openbossa.org> wrote:
> Hi Brian,
>
> On 11:39 Fri 18 Nov, Brian Gix wrote:
>>
>> LE does not have a Remote Name Request like BR/EDR has.  It does
>> have the ability to fairly efficiently request the remote device
>> name, however, which we should implement.  Currently the only
>> support we offer for obtaining the remote device name is to pluck it
>> out of the Advertising packets (Formatted identically to EIR) which
>> works for most devices, but as with BR/EDR, there is no requirement
>> that devices include their name in their advertising data.
>>
>> The Device Name characteristic is Mandatory, and may only exist once
>> for a device.  If it is less than 20 bytes may therefore be read
>> with a single ReadByType GATT command (uuid16: 0x2a00) over the full
>> 1-0xFFFF range. It must also be readable without security, so can be
>> done without first going through SMP.
>>
>> We may not want to featurize this particular functionality at all,
>> since all of the components to obtain this info is already
>> available: We just need to set up an ATT socket in BlueZ, and make
>> the request.  However, when we talk about Scanning for devices, and
>> automatically forwarding the Remote Name via a MGMT evevnt, the
>> precedence is there to supply it from the kernel.  And if we were to
>> go down that path, we would also want to simultaneously offer access
>> to the equally Mandatory and Unsecured "Appearance" Characteristic
>> (uuid16: 0x2a01) which is LE's sort-of equivilent to the BR/EDR
>> Class-Of-Device.
>>
>> So: What are the feelings about doing Remote Name (And Appearance)
>> discovery in the kernel, probably as part of the LE Discovery
>> mechanism?  I favor putting it in the kernel, due to the equivalent
>> functionality available to BR/EDR there.
>
> I am in favor of this, more because of the Appearance than the Name
> discovery. The Name most well behaved devices will provide through
> the Advertising Data, Appearance we can only discover via GATT and
> it is very useful for the user.
>
>>
>> Also, there is no coincidence that I offer this RFC at the same time
>> as I bring up the Write Signed Command functionality from earlier
>> today. Both concern usages of GATT (or at least ATT) in a way not
>> currently supported. It is also a case where ideally, we would use a
>> low-latency connect-read-disconnect methodology.
>>
>> --
>> Brian Gix
>> bgix@codeaurora.org
>> Employee of Qualcomm Innovation Center, Inc.
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
> Cheers,
> --
> Vinicius
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>

I really do not think this is a good idea. Forcing a connection while
scanning for devices is not a good idea for LE devices, which may
require a push button or some other user intervention to get
discoverable/connectable. Trying to connect to it while scanning may
cause it to stop being discoverable/connectable (if the device does
not become discoverable after disconnection), which will result in the
device either becoming non connectable, or require the user to press
the button again, which is making things more difficult and
complicated. I would suggest relying on the advertising data, and get
the remote name, or every other GAP related GATT characteristics once
a connection is established for the purpose it was supposed to be.

Best regards,
Chen Ganir

Re: [RFC] LE based Remote Name Request

[Claudio Takahasi]

Hi Brian/Vinicius,

On Fri, Nov 18, 2011 at 7:08 PM, Vinicius Costa Gomes
<vinicius.gomes@openbossa.org> wrote:
> Hi Brian,
>
> On 11:39 Fri 18 Nov, Brian Gix wrote:
>>
>> LE does not have a Remote Name Request like BR/EDR has.  It does
>> have the ability to fairly efficiently request the remote device
>> name, however, which we should implement.  Currently the only
>> support we offer for obtaining the remote device name is to pluck it
>> out of the Advertising packets (Formatted identically to EIR) which
>> works for most devices, but as with BR/EDR, there is no requirement
>> that devices include their name in their advertising data.
>>
>> The Device Name characteristic is Mandatory, and may only exist once
>> for a device.  If it is less than 20 bytes may therefore be read
>> with a single ReadByType GATT command (uuid16: 0x2a00) over the full
>> 1-0xFFFF range. It must also be readable without security, so can be
>> done without first going through SMP.
>>
>> We may not want to featurize this particular functionality at all,
>> since all of the components to obtain this info is already
>> available: We just need to set up an ATT socket in BlueZ, and make
>> the request.  However, when we talk about Scanning for devices, and
>> automatically forwarding the Remote Name via a MGMT evevnt, the
>> precedence is there to supply it from the kernel.  And if we were to
>> go down that path, we would also want to simultaneously offer access
>> to the equally Mandatory and Unsecured "Appearance" Characteristic
>> (uuid16: 0x2a01) which is LE's sort-of equivilent to the BR/EDR
>> Class-Of-Device.
>>
>> So: What are the feelings about doing Remote Name (And Appearance)
>> discovery in the kernel, probably as part of the LE Discovery
>> mechanism?  I favor putting it in the kernel, due to the equivalent
>> functionality available to BR/EDR there.
>
> I am in favor of this, more because of the Appearance than the Name
> discovery. The Name most well behaved devices will provide through
> the Advertising Data, Appearance we can only discover via GATT and
> it is very useful for the user.

IMO, the first attempt needs to be in the userspace. Name, Appearance
and *ServiceChanged* can be read on every reconnection. Appearance
will be exposed though adv data also, it is being discussed by the BT SIG.

If we implement the characteristic storage properly, I don't think we need
to read the Name and Appearance always since it will not change.

Another aspect against do it in the kernel as part of the discovery
procedure is "connectable and bondable mode", probably we will have
problems to re-connect. Peripherals may leave the bondable mode or
doesn't send advertises automatically after disconnection.

BR,
Claudio

>
>>
>> Also, there is no coincidence that I offer this RFC at the same time
>> as I bring up the Write Signed Command functionality from earlier
>> today. Both concern usages of GATT (or at least ATT) in a way not
>> currently supported. It is also a case where ideally, we would use a
>> low-latency connect-read-disconnect methodology.
>>
>> --
>> Brian Gix
>> bgix@codeaurora.org
>> Employee of Qualcomm Innovation Center, Inc.
>> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>
>
> Cheers,
> --
> Vinicius

Re: [RFC] LE based Remote Name Request

[Brian Gix]

Hi Chen, Claudio,

On 11/18/2011 2:30 PM, Claudio Takahasi wrote:
> Hi Brian/Vinicius,
>
> On Fri, Nov 18, 2011 at 7:08 PM, Vinicius Costa Gomes
> <vinicius.gomes@openbossa.org>  wrote:
>> Hi Brian,
>>
>> On 11:39 Fri 18 Nov, Brian Gix wrote:
>>>
>>> LE does not have a Remote Name Request like BR/EDR has.  It does
>>> have the ability to fairly efficiently request the remote device
>>> name, however, which we should implement.  Currently the only
>>> support we offer for obtaining the remote device name is to pluck it
>>> out of the Advertising packets (Formatted identically to EIR) which
>>> works for most devices, but as with BR/EDR, there is no requirement
>>> that devices include their name in their advertising data.
>>>
>>> The Device Name characteristic is Mandatory, and may only exist once
>>> for a device.  If it is less than 20 bytes may therefore be read
>>> with a single ReadByType GATT command (uuid16: 0x2a00) over the full
>>> 1-0xFFFF range. It must also be readable without security, so can be
>>> done without first going through SMP.
>>>
>>> We may not want to featurize this particular functionality at all,
>>> since all of the components to obtain this info is already
>>> available: We just need to set up an ATT socket in BlueZ, and make
>>> the request.  However, when we talk about Scanning for devices, and
>>> automatically forwarding the Remote Name via a MGMT evevnt, the
>>> precedence is there to supply it from the kernel.  And if we were to
>>> go down that path, we would also want to simultaneously offer access
>>> to the equally Mandatory and Unsecured "Appearance" Characteristic
>>> (uuid16: 0x2a01) which is LE's sort-of equivilent to the BR/EDR
>>> Class-Of-Device.
>>>
>>> So: What are the feelings about doing Remote Name (And Appearance)
>>> discovery in the kernel, probably as part of the LE Discovery
>>> mechanism?  I favor putting it in the kernel, due to the equivalent
>>> functionality available to BR/EDR there.
>>
>> I am in favor of this, more because of the Appearance than the Name
>> discovery. The Name most well behaved devices will provide through
>> the Advertising Data, Appearance we can only discover via GATT and
>> it is very useful for the user.
>
> IMO, the first attempt needs to be in the userspace. Name, Appearance
> and *ServiceChanged* can be read on every reconnection. Appearance
> will be exposed though adv data also, it is being discussed by the BT SIG.
>
> If we implement the characteristic storage properly, I don't think we need
> to read the Name and Appearance always since it will not change.
>
> Another aspect against do it in the kernel as part of the discovery
> procedure is "connectable and bondable mode", probably we will have
> problems to re-connect. Peripherals may leave the bondable mode or
> doesn't send advertises automatically after disconnection.

Those are otherwise good points (not all devices will automatically 
start advertising again) however ServiceChanged should never be 
attempted to be read.  We should only obtain this via an Indication from 
the remote device, and at any rate it is only shared with Trusted 
devices, so we would have to be Bonded.

However, I would definitely NOT try to re-read Name/Appearance at every 
connection.  Those should definitely be cached, and not re-read unless 
we get the ServiceChanged Indication.

Does anyone object to permanently deciding to NOT do Remote 
Name/Appearance request at device discovery time? Or in the kernel at 
all?  Particularly if the SIG is heading towards exposing the Appearance 
in Advertising data, this whole thing becomes nearly moot.  I agree with 
Chen and Claudio that attempting this at Discovery will likely cause the 
rare IOP problem, and the only drawback to Not doing it would be the 
rare BD Addr and no Appearance shown during scanning.

-- 
Brian Gix
bgix@codeaurora.org
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum

Re: [RFC] LE based Remote Name Request

[Chen Ganir]

On Sat, Nov 19, 2011 at 01:39, Brian Gix <bgix@codeaurora.org> wrote:
> Hi Chen, Claudio,
>
> On 11/18/2011 2:30 PM, Claudio Takahasi wrote:
>>
>> Hi Brian/Vinicius,
>>
>> On Fri, Nov 18, 2011 at 7:08 PM, Vinicius Costa Gomes
>> <vinicius.gomes@openbossa.org>  wrote:
>>>
>>> Hi Brian,
>>>
>>> On 11:39 Fri 18 Nov, Brian Gix wrote:
>>>>
>>>> LE does not have a Remote Name Request like BR/EDR has.  It does
>>>> have the ability to fairly efficiently request the remote device
>>>> name, however, which we should implement.  Currently the only
>>>> support we offer for obtaining the remote device name is to pluck it
>>>> out of the Advertising packets (Formatted identically to EIR) which
>>>> works for most devices, but as with BR/EDR, there is no requirement
>>>> that devices include their name in their advertising data.
>>>>
>>>> The Device Name characteristic is Mandatory, and may only exist once
>>>> for a device.  If it is less than 20 bytes may therefore be read
>>>> with a single ReadByType GATT command (uuid16: 0x2a00) over the full
>>>> 1-0xFFFF range. It must also be readable without security, so can be
>>>> done without first going through SMP.
>>>>
>>>> We may not want to featurize this particular functionality at all,
>>>> since all of the components to obtain this info is already
>>>> available: We just need to set up an ATT socket in BlueZ, and make
>>>> the request.  However, when we talk about Scanning for devices, and
>>>> automatically forwarding the Remote Name via a MGMT evevnt, the
>>>> precedence is there to supply it from the kernel.  And if we were to
>>>> go down that path, we would also want to simultaneously offer access
>>>> to the equally Mandatory and Unsecured "Appearance" Characteristic
>>>> (uuid16: 0x2a01) which is LE's sort-of equivilent to the BR/EDR
>>>> Class-Of-Device.
>>>>
>>>> So: What are the feelings about doing Remote Name (And Appearance)
>>>> discovery in the kernel, probably as part of the LE Discovery
>>>> mechanism?  I favor putting it in the kernel, due to the equivalent
>>>> functionality available to BR/EDR there.
>>>
>>> I am in favor of this, more because of the Appearance than the Name
>>> discovery. The Name most well behaved devices will provide through
>>> the Advertising Data, Appearance we can only discover via GATT and
>>> it is very useful for the user.
>>
>> IMO, the first attempt needs to be in the userspace. Name, Appearance
>> and *ServiceChanged* can be read on every reconnection. Appearance
>> will be exposed though adv data also, it is being discussed by the BT SIG.
>>
>> If we implement the characteristic storage properly, I don't think we need
>> to read the Name and Appearance always since it will not change.
>>
>> Another aspect against do it in the kernel as part of the discovery
>> procedure is "connectable and bondable mode", probably we will have
>> problems to re-connect. Peripherals may leave the bondable mode or
>> doesn't send advertises automatically after disconnection.
>
> Those are otherwise good points (not all devices will automatically start
> advertising again) however ServiceChanged should never be attempted to be
> read.  We should only obtain this via an Indication from the remote device,
> and at any rate it is only shared with Trusted devices, so we would have to
> be Bonded.
>
> However, I would definitely NOT try to re-read Name/Appearance at every
> connection.  Those should definitely be cached, and not re-read unless we
> get the ServiceChanged Indication.
>
ServiceChanged is irrelevant here. ServiceChanged will only notify you
if the handles changed, not if the value changed. Name and appearance
can and should be read, since we may get only the short name in the
advertising data, and we wil need the full name. In addition, a device
may change its name, and we will not be notified of this (GAP name
characteristic does not notify/indicate). Name may change just like it
does in BR/EDR.

> Does anyone object to permanently deciding to NOT do Remote Name/Appearance
> request at device discovery time? Or in the kernel at all?  Particularly if
> the SIG is heading towards exposing the Appearance in Advertising data, this
> whole thing becomes nearly moot.  I agree with Chen and Claudio that
> attempting this at Discovery will likely cause the rare IOP problem, and the
> only drawback to Not doing it would be the rare BD Addr and no Appearance
> shown during scanning.
>
> --
> Brian Gix
> bgix@codeaurora.org
> Employee of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum
> --
> To unsubscribe from this list: send the line "unsubscribe linux-bluetooth"
> in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>



Chen Ganir
chen.ganir@gmail.com

Re: [RFC] LE based Remote Name Request

[Brian Gix]

Hi Chen,

On 11/18/2011 9:28 PM, Chen Ganir wrote:
> On Sat, Nov 19, 2011 at 01:39, Brian Gix<bgix@codeaurora.org>  wrote:
>> Those are otherwise good points (not all devices will automatically start
>> advertising again) however ServiceChanged should never be attempted to be
>> read.  We should only obtain this via an Indication from the remote device,
>> and at any rate it is only shared with Trusted devices, so we would have to
>> be Bonded.
>>
>> However, I would definitely NOT try to re-read Name/Appearance at every
>> connection.  Those should definitely be cached, and not re-read unless we
>> get the ServiceChanged Indication.
>>
> ServiceChanged is irrelevant here. ServiceChanged will only notify you
> if the handles changed, not if the value changed. Name and appearance
> can and should be read, since we may get only the short name in the
> advertising data, and we wil need the full name. In addition, a device
> may change its name, and we will not be notified of this (GAP name
> characteristic does not notify/indicate). Name may change just like it
> does in BR/EDR.

I don't think we should do anything automatically on start-up.

If we know that we do not have the full name (if the Adv data has it 
flagged as "Partial") then we should of course fetch the full name from 
the characteristic.  However, if we get in the habit of re-reading data 
just because it *may* have changed, then we lose track of what LE is all 
about, which is minimization of over-the-air traffic.

If a particular high level app wants refresh the Name and/or Appearance, 
then of course which should provide that ability, but I might consider 
that App to be poorly written barring a compelling need, like perhaps an 
indication that it needs to be re-paired.  Single mode LE devices will 
generally be single mode because they want to limit these unneeded 
transactions.  LE Profiles are designed to not require Polling type 
activities, which a Name or Appearance refresh would be.

-- 
Brian Gix
bgix@codeaurora.org
Employee of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum